1. Field of the Invention
The invention concerns the production of glass in general from waste glass or glass batches. The three essential stations of the production process comprise melting, then refining and finally homogenizing.
2. Description of Related Art
The production of high-value special glasses requires the process step of refining after melting, in order to remove the residual bubbles from the melt. The prior art comprises the refining of glasses by addition of refining agents such as redox refining agents or evaporating refining agents. One speaks here of chemical refining, since the release of gases form the melt is utilized in order to inflate small bubbles that are present and thus to facilitate the rise of these bubbles.
Along with the methods of chemical refining, alternatively or additionally, physical effects are utilized, as described in the literature, for expelling bubbles and thus for refining, such as, for example, centrifugal force (U.S. Pat. No. 3,893,836) or the reduction of the bath depth and thus the rise of bubbles to the surface of the melt is facilitated (DE 197 10 351 C1).
It is known that refining is promoted by increasing the temperature of the melt. However, when refractory material is used for the refining tank, limits are imposed. If ceramics with high a zirconium content are used, then temperatures of a maximum 16,500° C. can be produced.
It is known also to conduct refining in an apparatus that operates according to the so-called skull pot principle. See EP 0 528,025 B1. Such a device comprises a crucible, the walls of which are formed from a ring or collar of metal pipes, which can be connected to a cooling medium, with slots between the metal pipes adjacent to one another. The device also contains an induction coil, which surrounds the walls of the crucible and by means of which high-frequency energy can be coupled into the contents of the crucible. This direct heating of the glass melt by means of irradiation of high-frequency energy is conducted at a power of 10 kHz to 5 MHz.
Such a crucible permits essentially higher temperatures than a vessel made of refractory material. The advantage of high-temperature refining in comparison to all other physical refining processes is that it is very effective and rapid due to the high temperatures. The processes take place clearly more rapidly at high temperatures, so that very small, rapid aggregate modules can be prepared for the process of refining.
DE 2,033,074A describes an arrangement for the continuous melting and refining of glass. A refining device is provided therein, which operates according to the skull pot principle. The melt from the bottom region of the melting vessel reaches the refining vessel via a connection channel. It enters in the bottom region of the latter. The glass flow in the refining vessel thus rises upward from the bottom. This has the advantage that the flow has the same direction as the lifting force of the bubbles. The bubbles to be removed reach the hot surface of the melt and are discharged from the latter.
A disadvantage of this embodiment consists of the fact that the connection channel between the melting-down basin and the high-frequency refining device is subject to intense wear and tear due to the high flow velocities.